Vertical centrifugal pumping apparatus are widely used for pumping liquids. The vertical centrifugal pump typically includes a pump body having an impeller which is housed within an impeller casing. The impeller is connected to the lower end of a rotary shaft. Operably connected to the upper end of the shaft is an electric motor, steam turbine or other prime mover which rotatably drives the shaft. Fluid entering the casing at the center of the impeller is radially displaced and pressurized by the rotating impeller. The pressurized fluid then exits the casing through an outlet located along the periphery of the casing.
Connected intermediate the pump body and motor is a tubular shaft column or housing. The rotary shaft extends through the column and enters the casing through an aperture in a back plate connected to the upward face of the impeller casing.
Fluid within the impeller casing must be prevented from flowing through the aperture upward along the shaft, toward the motor and leaking into the environment. The sealing about the shaft in the centrifugal pump is frequently accomplished with compressive stuffing, mechanical seals or dynamic seals such as expellers. The stuffing or seal is inserted in a stuffing chamber or box formed between the shaft and the pump housing rearward of the impeller.
When the centrifugal pump is handling abrasive slurry-type liquids, these conventional sealing methods have drawbacks. The stuffing requires a large amount of clean water as a continuous flush for the purposes of cooling and lubrication. Contact between an abrasive slurry liquid and mechanical seals subjects the seals to abrasive wear, thus leading to costly sudden failures.
Dynamic seals or expellers function while the impeller is rotating. When the impeller ceases to rotate, static head pressure due to the columns of liquid in the discharge and suction piping force fluid within the casing through the aperture and upwards between the shaft and column. Therefore, the dynamic seal requires a secondary seal such as a mechanical seal to prevent leakage when the pump is not running. However, contact between the abrasive slurry liquid and the mechanical seal will contaminate and destroy the effectiveness of the seal.
Therefore, it is a primary object of the present invention to provide an assembly for sealing about the rotary shaft of a vertical centrifugal pump when the shaft is both rotating and stationary.
Another object of the present invention is to provide a sealing device which does not require continuous flushing for cooling and lubrication.
A further object of the present invention is to provide a device which seals about a rotary shaft of the centrifugal pump when the pump is handling highly abrasive slurry-type liquids.